An unusually persistent harmful algal bloom (red tide) is currently affecting portions of the southwest coast of Florida. For the latest updates on this event, visit the Florida Fish and Wildlife Conservation Commission red tide status website or the NOAA Harmful Algal Bloom Bulletin.

If and when bloom the current bloom will end remains an open-ended question. Red tides can last as little as a few weeks or longer than a year. They can even subside and then reoccur. In 2005, for example, a bloom started off the coast of St. Petersburg, Florida, in January and then spread from there to Pensacola and Naples by October, persisting for the majority of the year. The duration of a bloom in nearshore Florida waters depends on physical and biological conditions that influence its growth and persistence, including sunlight, nutrients, and salinity, as well as the speed and direction of wind and water currents. Researchers are watching oceanographic conditions in the region carefully and using forecasting tools similar to seasonal weather forecasts to predict how long this bloom will last.

NOAA conducts scientific research and provides forecasts to give communities advance warnings to better deal with the adverse environmental impacts, health effects and economic losses associated with red tide and other harmful algal bloom events.

NOAA monitors conditions year round and provides official forecasts for red tide through two main products: conditions reports and bulletins. The conditions report identifies if red tide cell concentrations are present and provides forecasts of the highest potential level of respiratory irritation over the next three to four days. Bulletins provide decision-makers with a more in-depth analysis of the location of a current bloom and reported impacts, as well as forecasts of potential development, intensification, transport, and associated impacts of blooms. Both products are updated twice weekly during a bloom.

In addition, NOAA and a network of trained and authorized professionals from state and local organizations work together to respond to stranded marine animals found along the coastline during these events.

There are currently no means of controlling the occurrence of red tide.

The Florida red tide organism, Karenia brevis, produces potent neurotoxins, called brevetoxins, that can affect the central nervous system of many animals, causing them to die. That is why red tides are often associated with fish kills. Mortalities of other species, including manatees, dolphins, sea turtles, and birds also occur.

Wave action near beaches can break open K. brevis cells and release the toxins into the air, leading to respiratory irritation. For people with severe or chronic respiratory conditions, such as emphysema or asthma, red tide can cause serious illness. People with respiratory problems should avoid affected beaches during red tides.

Red tide toxins can also accumulate in filter-feeders mollusks such as oysters and clams, which can lead to Neurotoxic Shellfish Poisoning (NSP) in people who consume contaminated shellfish. While not fatal, NSP causes diarrhea and discomfort for about three days. Rigorous state monitoring of cells and toxins is conducted to close commercial shellfish harvesting if necessary to protect human health. Recreational shellfish harvesters should check State web pages to make sure it is safe to consume shellfish.

Some areas may be more affected than others. Check NOAA forecasts to assist in locating unaffected areas, and learn more about red tide health concerns from Florida Health.

This year’s bloom is different from what we’ve seen before in several ways:

Timing: Blooms of this alga typically start in late summer or early fall. The last large early summer bloom was in 2005. The current bloom started last fall and is still going.

Duration: While not unprecedented in its duration, this bloom is unusually persistent. It started in October 2017 and continued through spring of 2018. By early summer, the bloom resurged and was detected in five southwest Florida counties. Some shellfish harvesting areas have been closed since November 2017.

Size: The size of the bloom changes from week to week, and it is patchy. Not every beach is affected every day, so it is important to stay up to date with the NOAA conditions report. As of August 15, the bloom stretched from Pinellas County to Collier County, more than 150 miles.

While the timing, duration, and size of this red tide are unusual, red tides are not new to the Gulf Coast. Red tides were documented in the southern Gulf of Mexico as far back as the 1700s and along Florida’s Gulf coast in the 1840s. Fish kills near Tampa Bay were even mentioned in the records of Spanish explorers. For more information on historical red tide events in Florida, see the Florida Fish and Wildlife Conservation Commission’s harmful algal bloom monitoring database.

If you see sick, injured, or stranded wildlife, such as a sea turtle, manatee, dolphin, seabird, or a large fish kill in Florida, report it to the following standing network hotlines. To report an injured, hooked, entangled, or stranded sea turtle, call 1-877-942-5343. To report other sick or injured wildlife and fish kills, contact FWC Wildlife Alert or call 888-404-FWCC (888-404-3922). If you see dead or injured marine mammals, call 1-877-WHALE HELP (1-877-942-5343). You can also report via the Dolphin and Whale 911 Phone App.

There is no way to project the cumulative effects of this red tide event. Red tide occurs naturally in coastal waters of the Gulf of Mexico with blooms appearing seasonally. Although the Florida red tide organism, Karenia brevis, typically blooms between August and December, blooms often deviate from that time frame. The current bloom continues to be monitored by our local and state partners. Visit the Florida Fish and Wildlife Conservation Commission’s (FWC) red tide status page. Reports of fish kills and marine animal deaths are made publicly available on FWC’s website. For more information on the effects of red tide on marine animals, shellfish, and people, visit our health information page for more information.

While NOAA provides regional harmful algal bloom forecasts and supports research to better understand the causes, impacts, and effects of these events, we are not in a position to provide travel advice. We have provided links to Florida state resources in the right column of this announcement that we hope will help people make informed decisions about their travel plans.